1. Field of the Invention
The present invention relates to an illuminating device.
2. Description of the Related Art
Conventionally, an incandescent lamp or a fluorescent lamp has been typically used as a light source for general illumination, such as indoor lighting. Recently, the performance of a blue LED (light emitting diode) has been enhanced and so an LED is increasingly used also as a light source for a ceiling light, a down light, or the like (refer to, for example, Japanese Patent Application Laid-Open No. 2007-220465).
FIG. 7 shows what is called a pseudo white LED 100 that can be used as a light source for a lighting device. The pseudo white LED 100 includes: a blue LED 102 as a light emitting element; a lamp house 104 at a bottom of which the blue LED is disposed; and transparent resin 104 which seals a recess portion of the lamp house 104 and in which a yellow color fluorescent material 108, such as garnet (YAG), is dispersed.
A blue light emitted from the blue LED 102, while traveling through the transparent resin 106 disposed in the lamp house 104, is diffused, also at the same time is subjected to wavelength conversion by the yellow color fluorescent material 108 into a yellow color fluorescence, and then is emitted out of the lamp house 104 as exiting lights L (L1 and L2: illustrated by dashed double-dotted lines for the sake of convenience). In FIG. 7, reference number 103 refers to electrode terminals.
Also, the exiting lights L emitted from the pseudo white LED 100, when going through a lens sheet 110 arranged in front of the pseudo white LED 100, are deflected in the intended direction as illustrated in FIG. 8, whereby the pseudo white LED 100 is adapted to function as a light source for an illumination device.
Referring to FIG. 8, the lens sheet 110 includes: a first lens group 112 which is composed of refracting prisms and which is arranged inwardly to be located adjacent to an optical axis C of the pseudo white LED 100; and a second lens group 114 which is composed of reflecting prisms (TIR: total internal reflection) and which is arranged outwardly to be located away from the optical axis C of the pseudo white LED 100 so as to surround the first lens group 112.
The exit angles of the exiting lights L emitted from the pseudo white LED 100 are deflected by both the first lens group 112 and the second lens group 114 so as to travel in the direction parallel to the optical axis C.
In the illuminating device using the pseudo white LED 100 described above, however, the exiting lights emitted from the pseudo white LED 100 and located inwardly close to the optical axis C of the pseudo white LED 100 tend to be slightly tinged with a blue hue, while the exiting lights located at the fringe region away from the optical axis C of the pseudo white LED 100 tend to be slightly tinged with a yellow hue.
The above phenomenon is caused due to the fact that the exiting lights L2 which are directed obliquely with respect to the optical axis C of the pseudo white LED 100 travel through a longer light path in the transparent resin 106 having the yellow color fluorescent material 108 dispersed therein, compared to the exiting lights L1 which are directed parallel to the optical axis C of the pseudo white LED 100, which results in that the exiting lights L2 are more subjected to wavelength conversion by the yellow color fluorescent material 108 into yellow light fluorescence than the exiting lights L1.
The conventional illumination device using an incandescent lamp or a fluorescent lamp does not suffer such a color unevenness problem of illuminating light, which is inherent in the illumination device using the above described pseudo white LED 100 as a light source.
The present invention has been made in light of the problem described above, and it is an object of the present invention to provide an illumination device using a pseudo white LED in which a degree of color unevenness is reduced without impairing the brightness of illumination light.
The embodiment shown in the following description of the invention is presented to exemplify a configuration according to the present invention and provide an explanation on an aspect-by-aspect basis for the purpose of facilitating understanding of a diversity of the configuration of the present invention. Each aspect does not limit the technical scope of the present invention, and modifications developed by replacing, eliminating a part of the constituent elements of each aspect, or further by adding some other constituent elements thereto are included in the technical scope of the present invention.
In order to achieve the object described above, according to a first aspect of the present invention, there is provided an illuminating device including: a light source which includes a light emitting element and a fluorescent material; and a lens sheet which includes a plurality of prisms arranged symmetrically with respect to the optical axis of the light source, and which at least includes a first lens group located adjacent to the optical axis of the light source and a second lens group located outside the first lens group, wherein the first lens group includes a plurality of prisms each having an inclined face facing toward the optical axis of the light source.
In the illuminating device according to the first aspect, when exiting lights emitted from the light source come out from the lens sheet, the optical paths of the exiting lights are deflected in a direction opposite to the optical axis of the light source by means of the plurality of prisms which are included in the first lens group located at a portion of the lens sheet adjacent to the optical axis of the light source, which are arranged symmetrically with respect to the optical axis of the light source, and each of which has the inclined face facing toward the optical axis of the light source.
Here, if, when controlling the direction of the deflection, the heights of the prisms are increased so as to change the inclination angle of the inclined face in accordance with the distance from the optical axis of the light source, the area of a face (parallel face) of the prism oriented parallel to the optical axis of the light source is increased.
However, since the inclined faces of the prisms of the first lens group face toward the optical axis of the light source, the exiting lights emitted from the light source do not enter directly the parallel face of the prism, and thus the utilization efficiency of light is not lowered. And, the exiting lights emitted from the light source and coming out via the first lens group of the lens sheet are adapted to mix with the exiting lights emitted from the light source and coming out via the second lens group located outside the first lens group.
According to a second aspect of the present invention, in the illuminating device as described above in the first aspect, the plurality of prisms included in the first lens group may be configured such that respective inclination angles of the inclined faces decrease with an increase in distance from the optical axis of the light source.
In the illuminating device according to the second aspect, the plurality of prisms included in the first lens group are configured such that respective inclination angles of the inclined faces decrease with an increase in distance from the optical axis of the light source, whereby the direction of deflection can be controlled in accordance with the distance from the optical axis of the light source by means of the plurality of the prisms included in the first lens group.
Specifically, for example, the inclination angles of the inclined faces are configured to decrease with an increase in distance from the optical axis of the light source so that the exit angles of the exiting lights emitted from the light source and coming out via the first lens group of the lens sheet are uniform independent of the distance from the optical axis of the light source.
According to a third aspect of the present invention, in the illuminating device as described above in the first and second aspects, the second lens group may include a plurality of reflecting prisms.
In the illuminating device according to the third aspect, since the second lens group includes the plurality of reflecting prisms, the exiting lights which are emitted from the light source and come out via the second lens group are deflected, in a region of the lens sheet located outside the first lens group, so as to travel in the direction parallel to or approaching the optical axis of the light source.
Accordingly, the exiting lights emitted from the light source and coming out via the first lens group can be well mixed with the exiting lights emitted from the light source and coming out via the second lens group located outside the first lens group.
According to a fourth aspect of the present invention, in the illuminating device as described above in the third aspect, a third lens group, which includes a plurality of prisms each having an inclined face facing in the direction opposite to the optical axis of the light source, may be provided and located between the first lens group and the second lens group.
In the illuminating device according to the fourth aspect, the exiting lights emitted from the light source are deflected also by the third lens group. Since the inclined faces of the prisms included in the third lens group face in the direction opposite to the optical axis of the light source, the exiting lights emitted from the light source and entering the third lens group are refracted at the inclined faces of the prisms and thereby deflected so as to travel in the direction toward (which is the opposite direction compared to the deflection of the exiting lights coming out via the first lens group) or parallel to the optical axis of the light source.
And, the exiting lights emitted from the light source and coming out via the first lens group, the exiting lights emitted from the light source and coming out via the second lens group and the exiting lights emitted from the light source and coming out via the third lens group arranged between the first and second lens groups are adapted to mix with one another thereby achieving further color mix.
According to a fifth aspect of the present invention, in the illuminating device as described above in the first and second aspects, the second lens group may include a plurality of prisms each having an inclined face facing in the direction opposite to the optical axis of the light source.
In the illuminating device according to the fifth aspect, since the inclined faces of the plurality of prisms included in the second lens group are configured to face in the direction opposite to the optical axis of the light source, the exiting lights emitted from the light source and entering the second lens group are refracted at the inclined faces of the prisms in a region of the lens sheet located outside the first lens group, and are thereby deflected so as to travel in the direction toward (which is the opposite direction compared to the deflection of the exiting lights coming out via the first lens group) or parallel to the optical axis of the light source.
Accordingly, the exiting lights emitted from the light source and coming out via the first lens group can be well mixed with the exiting lights which are emitted from the light source and come out via the second lens group located outside the first lens group.
According to a sixth aspect of the present invention, in the illuminating device as described above in any one of the first to fifth aspects, the plurality of the prisms included in each of the first, second and third lens groups may be arranged rotationally symmetrically with respect to the optical axis of the light source.
In the illuminating device according to the sixth aspect, since the plurality of the prisms included in the respective lens groups are arranged rotationally symmetrically with respect to the optical axis of the light source, the exiting lights emitted from the light source and coming out via lens sheet can be well mixed with respect to all the radial directions around the optical axis of the light source 12.
According to a seventh aspect of the present invention, in the illuminating device as described above in any one of the first to sixth aspects, the light emitting element may be a blue light emitting diode (LED), wherein the fluorescent material causes a blue light emitted from the blue LED to be subjected to wavelength conversion into a yellow color fluorescence.
In the illuminating device according to the seven aspect, the blue light emitted from the blue LED is subjected to wavelength conversion by the fluorescent material into a yellow color fluorescence, thus a pseudo white LED.
And, the exiting lights emitted from the pseudo white LED are well mixed with one another by means of the prisms of the lens sheet as described above, and thereby the color unevenness inherent to the pseudo white 100 can be reduced or even overcome.